Finding the Fourth Proportional to 1,369.98, 1,890.76 and 780.57

Step by Step Solution

1. Step 1: Write the proportion equation
   1,369.98 : 1,890.76 = 780.57 : x
2. Step 2: Convert to fraction form
   1,369.98/1,890.76 = 780.57/x
3. Step 3: Cross multiply
   1,369.98x = 1,890.76 × 780.57
4. Step 4: Simplify right side
   1,369.98x = 1,475,870.53
5. Step 5: Solve for x
   x = 1,475,870.53/1,369.98
6. Step 6: Final answer
   x = 1,077.29